1. Field of the Invention
The present invention relates to apparatus and processes for drilling multiple subterranean wells and for completing such wells via separate casings, and more particularly, to apparatus and process for drilling and completing such multiple wells which will allow such wells to be deviated at significant degrees of separation and/or to be drilled into and completed within separate subterranean formations or zones having varying reservoir pressure characteristics.
2. Description of Related Art
Increasingly, well bores are being drilled into subterranean formations at an orientation which is purposely deviated from true vertical by means of conventional whipstock technology or a mud motor secured in the drill string adjacent the drill bit. In fractured subterranean formations, deviated wells are utilized to increase the area of drainage defined by the well within the subterranean formation, and thus, increase production of hydrocarbons from the subterranean formation. An inherent problem in utilizing a conventional whipstock to drill a deviated well is that both the depth and radial orientation of the whipstock is set when the whipstock is positioned in the well bore and cannot be changed without retrieving the whipstock from the well bore and changing the depth and/or radial orientation thereof.
In addition, wells drilled from offshore drilling platforms are usually deviated to increase the number of wells which can be drilled and completed from a single platform. Offshore drilling platforms which are utilized in deep water to drill and complete wells in a subterranean formation vary in size, structure, and cost depending upon the water depth and the loads in which the platform will be set. For example, a platform may be constructed to be supported in part by one leg or caisson which extends to the ocean floor or by as many as eight such legs or caissons. Costs of such offshore drilling platforms vary from approximately $5,000,000 to $500,000,000. Each offshore drilling platform is equipped with a set number of slots via which deviated wells can be drilled and completed through surface casing which is secured at the mudline by conventional techniques.
Due to the significant capital expenditure required for these offshore platforms, templates and processes for drilling and completing multiple wells via a single surface or intermediate casing have been developed. To achieve the most economic development of subterranean hydrocarbon reserves, it may be desirable to drill and complete wells into distinct subterranean formations or zones which can be located at depths differing by up to 10,000 feet or more. Subterranean formations or zones of differing depths often contain fluids at greatly differing pressures which are produced therefrom at significantly different flow rates. Although the templates which have been developed can be utilized to drill and complete subterranean wells into distinct formations or zones of varying depths, these templates are not designed to accommodate casing of a diameter, e.g. 7 inches, which is sufficient to enable fluids to be produced at a rate and/or volume necessary to render a relatively deep well profitable. Thus, a need exists for apparatus and processes to drill and complete multiple subterranean wells from a well bore into a plurality of subterranean formations or zones at differing depths. A further need exists for an apparatus and process to drill and complete multiple subterranean well bores at greater degrees of separation from each other thereby significantly increasing the area of drainage and thus enhancing hydrocarbon recovery from the well.
Accordingly, it is an object of the present invention to provide a template and process for drilling and completing multiple subterranean wells to significantly different true vertical depths via a single surface or intermediate casing and for completing such multiple wells via separate casings positioned through the surface or intermediate casing.
It is another object of the present invention to complete such multiple, cased wells in a manner such that remedial operations can be conducted on one well while hydrocarbons from a subterranean formation or zone are simultaneously being produced from the other wells which are completed via separate casings positioned within the same surface or intermediate casing.
It is still another object of the present invention to provide a surface template and process for drilling multiple cased wells which have a high degree of separation without the use of a whipstock.
It is a further object of the present invention to provide such a template for drilling multiple cased wells which is relatively simple in construction, which permits casing of each multiple well to separately depend from the template, and which provides that separate casing of each multiple well may extend to the surface.
It is a still further object of the present invention to provide a template and process for drilling and completing multiple subterranean wells from a single surface or intermediate casing wherein at least one well of the multiple subterranean wells is drilled and completed to significantly greater depths than previously obtainable.
It is a still further object of the present invention to utilize a downhole or subsurface template to drill and/or complete multiple subterranean wells from a tubular of a multiwell surface template which is positioned in a subterranean environment.